Published in Petroleum Transactions, AIME, Volume 210, 1957, pages 295–301. Abstract This paper describes a technique which permits visual observation of oil displacement processes throughout the interior of a porous structure as thick as two inches. A model having glass walls is filled with finely powdered glass. Such a model becomes completely transparent if the powdered glass pack is saturated with an oil having the same refractive index as the glass. When water or gas, with a refractive index different from that of the oil (glass) is injected, the model becomes opaque in the space occupied by the water (gas). Visual observation and photography of these displacement processes are thus rendered possible. The following processes have been studied:Displacement of oil by water (linear drive) in a homogeneous formation, in a stratified formation.Water flooding (five-spot well pattern).Solution gas-drive process.Oil-bank formation. Introduction Most of the scaled model experiments heretofore carried out in the Koninklijke/Shell Laboratorium, Amsterdam, have been done in steel containers, saturated sand packs being used to represent the oil bearing formation. In such experiments, for instance those on the displacement of oil by water, the cumulative oil production was measured as a function of the cumulative water injection. In order to interpret the measured production data, a need has for some time been felt for a means of observing visually what happens in the course of such experiments. Some information of this type was obtained earlier by observing the water oil distribution in various cross sections of the sand after the conclusion of the experiment. However, the technique used did not guarantee that the fluid distribution remained undisturbed. Moreover, the procedure was somewhat elaborate and the information obtained limited. Therefore a new technique has been developed, which is described below.